Under Armour, a rookie company that’s revolutionizing the market for performance sports apparel, is challenging larger rivals like Nike and Reebok in a series of television advertisements airing this month on ESPN and MTV.

In 15- and 30-second spots set to run during the MTV Music Video Awards last night, a captain leads his teammates in a chant.

“Will you protect this house?” the captain asks – house is sports lingo for home field.

The team’s response: “I will. I will.”

The subtext is laden with references to giant sporting goods companies like Nike and Reebok, which are trying to muscle in on Under Armour’s home turf: the fast-growing market for specially treated performance apparel that’s supposed to wick away sweat and keep athletes dry.

“Under Armour was the innovator, and it remains the leader,” said Mark Hoffman of SportScanInfo, a market research firm.

“But there are a lot of companies looking to get into this business. It’s as though Under Armour has a bull’s eye painted on it.”

The market for this type of apparel grew 67 percent in the last year, to nearly $150 million, according to SportScanInfo.

Under Armour has by far the largest share, with a 66 percent stake. Nike’s share stands at 3.4 percent and Reebok’s at 1.2 percent.

Based in Baltimore, Under Armour was started by Kevin Plank, who’d had it with sweaty t-shirts during football practice at the University of Maryland.

Just before graduation in 1996, Plank, now 31, maxed out five credit cards to raise $40,000, and created a line of shirts, shorts and underwear designed to keep athletes dry.

He sent the garments to a few of his former teammates who’d gone on to play in the NFL – including Heisman Trophy winner Eddie George.

The first big break came when Plank sent samples of his clothes to the set of “Any Given Sunday,” the 1999 movie staring Al Pacino.

Director Oliver Stone saw the gear and liked the logo. But there was a hitch: Plank’s company was so small it lacked the money to produce the goods unless it got paid.

Companies typically supply merchandise to movie sets free of charge in exchange for the advertising bonanza of a product placement. In an unusual move, Stone agreed to pay $12,000 for the merchandise.

Today, with $115 million in annual sales, Under Armour has become an established player.

“We can’t keep their men’s briefs on the shelves,” Doug Morton, chief executive of the Sports Authority, told The Post.

He said sales of Under Armour garments at his 389 stores have increased 300 percent in the last six months alone.

It’s unclear how long Under Armour can maintain its David-like lead in the face of deeper-pocketed Goliaths.

Reebok’s NFL Equipment line goes head-to-head with Under Armour, and Reebok recently signed a 10-year, $250 million agreement with the NFL that prevents players from displaying competing logos.

“We created this category,” Plank told The Post, “and now everyone’s trying to take us on.”